The Science Behind Lithium Cell Characteristics And Safety

September 18, 2017 by Sean Boyce 58 Comments

To describe the constraints on developing consumer battery technology as ‘challenging’ is an enormous understatement. The ideal rechargeable battery has conflicting properties – it has to store large amounts of energy, safely release or absorb large amounts of it on demand, and must be unable to release that energy upon failure. It also has to be cheap, nontoxic, lightweight, and scalable.

As a result, consumer battery technologies represent a compromise between competing goals. Modern rechargeable lithium batteries are no exception, although overall they are a marvel of engineering. Mobile technology would not be anywhere near as good as it is today without them. We’re not saying you cannot have cellphones based on lead-acid batteries (in fact the Motorola 2600 ‘Bag Phone’ was one), but you had better have large pockets. Also a stout belt or… some type of harness? It turns out lead is heavy.

The Motorola 2600 ‘bag phone’, with a lead-acid battery. Image CC-BY-SA 3.0 source: Trent021

Rechargeable lithium cells have evolved tremendously over the years since their commercial release in 1991. Early on in their development, small grains plated with lithium metal were used, which had several disadvantages including loss of cell capacity over time, internal short circuits, and fairly high levels of heat generation. To solve these problems, there were two main approaches: the use of polymer electrolytes, and the use of graphite electrodes to contain the lithium ions rather than use lithium metal. From these two approaches, lithium-ion (Li-ion) and lithium-polymer (Li-Po) cells were developed (Vincent, 2009, p. 163). Since then, many different chemistries have been developed.

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Chest Of Drawers Stores Audio Memories

September 18, 2017 by Dan Maloney 15 Comments

Some people collect stamps, some collect barbed wire, and some people even collect little bits of silicon and plastic. But the charmingly named [videoschmideo] collects memories, mostly of his travels around the world with his wife. Trinkets and treasures are easy to keep track of, but he found that storing the audio clips he collects a bit more challenging. Until he built this audio memory chest, that is.

Granted, you might not be a collector of something as intangible as audio files, and even if you are, it seems like Google Drive or Dropbox might be the more sensible place to store them. But the sensible way isn’t always the best way, and we really like this idea. Starting with what looks like an old card catalog file — hands up if you’ve ever greedily eyed a defunct card catalog in a library and wondered if it would fit in your shop for parts storage — [videoschmideo] outfitted 16 drawers with sensors to detect when they’re opened. Two of the drawers were replaced by speaker grilles, and an SD card stores all the audio files. When a drawer is opened, a random clip from that memory is played while you look through the seashells, postcards, and what-have-yous. Extra points for using an old-school typewriter for the drawer labels, and for using old card catalog cards for the playlists.

This is a simple idea, but a powerful one, and we really like the execution here. This one manages to simultaneously put us in the mood for some world travel and a trip to a real library.

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A Jet Engine On A Bike. What’s The Worst That Could Happen?

September 18, 2017 by James Hobson 76 Comments

On today’s edition of ‘don’t try this at home,’ we’re transported to Russia to see [Igor Negoda]’s working jet bicycle.

This standard mountain bike comes equipped with a jet engine capable of 18kg of thrust, fixed to the frame under the seat with an adjustable bracket to change it’s angle as needed. A cell phone is zip-tied to the frame and acts as a speedometer — if it works, it’s not stupid — and an engine controller displays thrust, rpm and temperature. A LiPo battery is the engine’s power source with a separate, smaller battery for the electronics. The bike is virtually overgrown with wires and tubes that feed the engine, including an auxiliary fuel tank where a water bottle normally resides. Where’s the main fuel tank? In [Negoda]’s backpack, of course.

It certainly kicks up a mean dust cloud and makes a heck of a racket but the real question is: how fast does it go? From the looks of the smartphone, 72 km/h, 45 mph, or 18 rods to the hogshead.

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